Abstract—A hypabyssal intrusive of fayalite plagiogranites of Mount Kastel intruded into the Yuzhnoberezhny uplift of the Gorno-Crimean tectonic Zone of the Crimean Cimmerids. Plagiogranites cross and contact metamorphosed intensivly dislocated flysch strata of the Taurian series T2 –J1, the bodies of island arc gabbroids of the Early Bajocian Pervomaisko–Ayudag complex, and basalts of the Late Bajocian Karadag volcanic series. Judging by the fracture pattern and the nature of the contacts, the intrusive is relatively weakly tectonized. Post-arc plagiogranites of the Mount Kastel intrusive (SiO2 72.02 wt %; Na2O, 4.57; K2O, 1.26; Na2O : K2O = 3.6; ferrugious rocks – 92.4%; Th ⪢ U) contain high Fe olivine—fayalite and ferrohortonolite, eulite, and annite, as well as abundant accessory, zircon, monazite-Ce, xenotime-Y. In crystallization differentiation of plagiogranites in the Kastel intrusive, Fe and Mn accumulated in olivine, Na and K in plagioclase, Mn in ilmenite, Hf in zircon, and Th in monazite; the field of solid solutions of zircon and xenotime narrowed. Endemic fayalite plagiogranites could have arisen under the conditions of an orogenic regime, which apparently follows the geological history of the Crimean Cimmerids.